Purification device for alkali metal electrolysis cells



Aug. 26, 1969 L. l... HARRIS 3,463,721

PURIFICATION DEVICE FOR ALKALI METAL ELECTROLYSIS CELLS Filed March 3,1967 2 Sheets-Sheet 1 FIG. 2.

6,1969 L. L. mms 3,463,721

PURIFICATION DEVICE FOR ALKALI METAL E LECTROLYSIS CELLS Filed March a,1967 2 Sheets-Sheet 2 United States Patent 3,463,721 PURIFICATION DEVICEFOR ALKALI METAL ELECTROLYSIS CELLS Luther L. Harris, La Porte, Tex.,assignor to Ethyl Corporation, New York, N.Y., a corporation of VirginiaFiled Mar. 3, 1967, Ser. No. 620,482 Int. Cl. C22d 3/02 US. Cl. 204-2457 Claims ABSTRACT OF THE DISCLOSURE Apparatus for removing undesiredmetal deposits from product and product conduit walls of fused meltelectrolysis cells. A rotatable central shaft supports vertically spacedhorizontal arms having radial extensions. Vertical scraper bars aremovably mounted on the ends of said radial extensions.

Background of the invention Generally, cells for the production ofalkali metals are of a type basically similar in design to the Downscell, US. Patent 1,501,756. This cell is characterized by abottom-mounted carbon anode surrounded by a cylindrical steel cathode.Within the annular portion formed between the anode and cathode aforaminous metal diaphragm is inserted usually. During electrolysis,chlorine is evolved from the anode and is removed from the upper portionof the cell through a gas dome situated above the anode, and alkalimetal, or sodium, which is separated from the salt solution electrolyte,is displaced to the upper portion of the cell, manifolded within anannular collecting chamber and removed through a vertical take-off lineor riser pipe communicating with the cell exterior.

Because of the high temperature required to melt alkali metals salts,particularly sodium chloride, it is customary to add a second saltthereto to lower the melting point of the electrolyte mixture.Generally, a fused mixture of calcium chloride and sodium chloride isemployed for the manufacture of sodium. This necessitates a separationof calcium metal from the product sodium metal, and a major portion ofthe calcium metal is removed by passing the sodium metal upward througha cool riser pipe prior to discharge. The sodium metal solution coolsgradually during its upward ascent causing precipitation of calciummetal from the molten sodium. Most of the calcium metal precipitatedfalls or is returned to the bottom of the electrolytic cell where itdissolves; however, some calcium metal is deposited on the inner wall ofthe riser pipe. Such deposits, if not removed, will eventually causecomplete plugging of the riser pipe, and it is, therefore, essentialthat these deposits be removed. customarily, tickler devices are used todislodge calcium deposits in riser pipes of sodium cells andautomatically operated tickler devices are described, for example, inU.S. Patents 2,770,364, 2,770,592, 2,861,938 and 2,944,955. Thesedevices usually comprise a cleaner assembly operatively connected to adrive mechanism. The cleaner assembly usually consists of a plurality ofcleaner blades or scrapers mounted so as to act upon the inner wall ofthe riser pipe, generally over its entire length, and to dislodgeforming, or already formed, calcium deposits. Generally, the blades orscrapers are allixed to a shaft whose axis of rotation corresponds tothe center of the riser pipe and extends therethrough. The shaft andaffixed scraper bar generally are capable of rotation around the axis ofrotation and of limited vertical movement along the axis.

Various drive mechanisms have been proposed for these devices; however,there is a common tendency for "ice all devices to function for alimited period and then to fail due to their inability to withstand theoperating condition or to remove successfully all deposits. After atickler fails, or ceases to function, a new cleaner assembly must beinserted into an operating cell. The duration of time within which atickler will continue to function properly before it must be removedfrom the cell is referred to as tickler life, and for present commercialticklers this service period is of extremely short duration. When anautomatic tickler fails to function, it is essential that the tickler beplaced back in operation promptly to prevent a complete plugging of theriser pipe. Should this occur the blockage must be chipped away by handand a new cleaner assembly placed in the operating cell. A commercialinstallation for producing sodium contains a large number of individualcells and the cleaning of riser pipes and replacement of ticklers is acostly operation. Therefore, extension of tickler life means largesavings in labor and material costs, and obviously, the extension oftickler life is a very desirable goal.

Accordingly, it is an object of this invention to provide a new andimproved tickler or cleaning assembly capable of operation for extendedperiods of time without failure. It is also an object of this inventionto provide a new and improved tickler which will decrease operating costgreatly. A further object of this invention is to provide an apparatusmore simple in construction and effective in cleaning riser pipe wallsthan has heretofore been possible.

Summary of invention These and other objects are accomplished inaccordance with this invention, in a fused salt electrolysis cell havinga riser pipe extending above the cell for concurrently dischargingsodium metal and for cooling, precipitating and returning to the cellcalcium impurity contained therein, said riser pipe having a ticklerassembly in combination therewith which includes a cleaning deviceextending into said riser pipe and driving means operably connectedtherewith for at least rotating said cleaning device, by an improvedcleaning device comprising, in combination,

(a) A rotatable elongated member extending centrally and substantiallyvertically from substantially the bottom through the top of said riserpipe for operable connection with said driving means,

(b) At least two arms mounted in vertical spaced relationshisubstantially horizontally on and extending radially from said elongatedmember, and

(c) At least one vertical scraper bar .movably mounted on the radialextension of a vertically adjacent pair of said at least two arms andextending therebetween, said at least one vertical scraper bar beingconstructed and arranged to have one vertical side move toward saidriser pipe when said elongated member is rotated in one direction andsaid one vertical side move away from said riser pipe when saidelongated member is rotated in the op posite direction.

A preferred embodiment of the invention is the apparatus described abovefurther characterized by said one vertical side being provided with asubstantially knife-like edge.

Another preferred embodiment is the apparatus described above furthercharacterized by having a plurality of vertical scraper bars attached toa plurality of arms 7 and spaced alternately on opposite sides of saidrotatable said at least two arms extending in the same radial directionfrom said rotatable elongated member.

And another preferred embodiment is the apparatus described abovefurther characterized by said at least two arms being slottedhorizontally for mounting said at least one scraper bar.

A further preferred embodiment of the invention is the apparatusdescribed above further characterized by the vertical scraper barclosest to the bottom of said riser pipe being rigidly affixed to saidarms.

A still further preferred embodiment of the invention is the apparatusdescribed above further characterized by said at least two arms havingmeans for restricting the movement of said at least one vertical sideaway from said riser pipe.

Brief description of the drawing The details of the apparatus and of apreferred embodiment will be more readily understood from the followingdescription and by reference to the accompanying drawing having FIGS.l-4 wherein:

FIG. 1 is a generalized elevation illustrating the relation of theapparatus of this invention to a fused salt electrolysis cell for whichit is intended.

FIG. 2 is an elevation, in partial cross section and on a larger scale,of a cell riser pipe having the apparatus bf this invention incorporatedtherein, and

FIG. 3 is a sketch showing the assembly of at least one section of theapparatus of this invention.

FIG. 4 is a cross section 22 of FIG. 2 showing the movement of thescraper bars of the apparatus of this invention in greater detail.

Description of a preferred embodiment Referring first to FIG. 1, theprincipal parts of an electrolytic cell for the production of sodium andchlorine from a molten mixture of at least sodium chloride and calciumchloride include a cell body 11 comprising an external steel shell linedwith refractory brick, a centrally mounted carbon anode 12 surrounded bya cylindrical cathode 13 having lugs 14 projecting through the cellwalls to provide for connection to bus bars 15 for supply of electriccurrent. Similarly, current is fed to anode 12 by an anode bus bar 16.Dome and collector assembly 17 is mounted centrally above theanode-cathode electrodes and includes a chlorine dome 18 in the form ofa generally cylindrical member and a sodium collecting conduit 19. Thechlorine dome terminates in a chlorine discharge line 20 to transfergaseous chlorine to subsequent operations. Sodium collecting conduit 19meets and is connected with riser pipe 21, shown in this figure in anexternal view, which is an elongated steel tube which may be providedwith fins 22 or other means on at least a portion of the externalsurface. Surmounting riser pipe 21 is a guiding and actuating assembly23 for supporting and moving the apparatus of this invention.

As shown in FIG. 2, molten sodium may be discharged from the cell at thetop portion of riser pipe 21, over wier 25 into receiving box 26 mountedadjacent to riser pipe 21. Receiver box 26 provides a container fortemporary recovery of produced sodium which may be collectedsubsequently in a transfer vessel or container not shown, from dischargespout 27.

In operation, bath 31 contains molten electrolyte chlorides to a levelabove the bottom of chlorine dome 18 and sodium conduit 19 andintermediate the full vertical elevation of chlorine dome 18. The moltenelectrolyte chlorides generally include sodium chloride and appreciablequantities of calcium chloride to reduce the melting point of the sodiumchloride. A sodium-calcium mixture and chlorine are produced in theannular space between anode 12 and cathode 13 and rise on opposite sidesof diaphragm 32. The sodium-calcium mixture collects in channel 19 andflows to the entrance of riser pipe 21, rises in the riser pipe and isdischarged over wier 25 to receiver 26 for subsequent collection fromdischarge spout 27. Cooling of the sodium-calcium mixture in the riserpipe precipitates calcium from the mixture and a major portion thereoffalls down through the rising mixture to be returned to the cell;however, a noticeable quantity tends to deposit on the interior walls ofthe riser pipe.

Details of the construction and the method of operation of the improvedcleaning device of this invention will be more readily understood byreference to FIG. 2. Guiding and actuating assembly 23 located on top ofriser pipe 21 carries and rotatably supports central shaft 41 anddriving means 44 for the shaft. In the embodiment described, drivingmeans 44 is manual, however, it is clear that such means may bepneumatic of electrically driven or a combination of such devices. Apreferred pneumatic device driving means is described fully in US.Letters Patent 2,770,364.

Located in vertically spaced relationship on central shaft 41 aresubstantially horizontal arms 42 having radial extensions 45. In thepreferred embodiment of FIG. 2, a plurality of arms are shown, however,it is clear that only at least two are necessary for the apparatus andmethod of the invention. Movably mounted on the radial extension of avertically adjacent pair of arms 42 are vertical scraper bars 46.Scraper bar 46 may be provided in suflicient length so that the cleaningpath of one bar overlaps the cleaning path of the bar immediately aboveand below, and it is clear also that in an embodiment having only twoarms only one vertical scraper bar would be required. In an embodimenthaving two arms and one scraper bar or more than two arms and two ormore scraper bars, it is clear that it is not necessary that the scraperbar be located vertically. It is within the scope of the invention thatthe arms and the radial extensions thereof may be located on shaft 41 ata position such that the radial extensions of the arms do not lie withinthe same vertical plane. In this embodiment, suitable connections may beprovided to locate the movable scraper bar or bars between verticallyadjacent arms not in the same vertical plane.

Referring now to FIG. 3, horizontal arm 42 consists of an upper section47 and a lower section 48 for securing and movably mounting verticalscraper bar 46. For the assembly of the apparatus, vertical scraper bar46, having knife-like edge 49, is joined securely by welding or othersuitable means to support plates 50 with plates 50 being located on bar49 with a proper distance between them to provide for sliding to theassembly freely into the horizontal slot between upper and lowersections 47 and 48 on a vertically adjacent pair of arms 42. Attached toeach plate 50, is a stop bar 51 provided in a length sufiicient tooverlap sections 47 and 48 when assembled. Fixed stop bar 52 is fixedlylocated by welding or other means on arm 42 across the slot betweensections 47 and 48 to restrict the movement of plate 50 in a horizontaldirection toward shaft 41 and to prevent the inadvertent disassembly ofthe apparatus. After locating the assembled vertical scraper bar,horizontal plates 50 and stop bar freely within the slotted area betweensections 47 and 48 on a vertically adjacent pair of arms 42, end plate53 supported by beam 54 is fixedly attached across the radial ends ofsections 47 and 48; to prevent the disengagement of the vertical scraperar assembly from the apparatus during the insertion and removal of theimproved cleaning device from riser pipe 21 and during operationthereof. If necessary or desired, one or more scraper bars may berigidly attached to a pair of arms 42 or to one or more permanent armsas indicated at 55.

The method of operation of the improved cleaning device of thisinvention may be understood more clearly by reference to FIG. 4 which isa cross section 2-2 of FIG. 2 enlarged. As can be seen on FIG. 4, whenshaft 41 is rotated in a counterclockwise direction, scraper bar 46contacts the inside wall of riser pipe 21 at its knifelike edge 49sweeping away deposited material which may then fall freely to thebottom of the riser pipe for return to the cell. When shaft 41 isstopped or is rotated in the opposite direction, the scraper bar, andthe parts fixedly attached, move toward the shaft in position Withinriser pipe 21 to permit easy removal and insertion of the improvedcleaning device. It is clear that a scraper bar assembly may be attachedto the arms in a manner so that the cleaning device may be operable byrotation in either or both directions and vertical movement may be madeof the entire cleaning device during operation also.

Any suitable material or materials which will Withstand the serviceconditions of temperature and contacting materials of the applicationfor the cleaning device are suitable for the construction of theimproved cleaning device of this invention. When the improved cleaningdevice is used in the riser pipe a fused salt electrolysis cell for themanufacture of sodium and chlorine, it is preferred that this apparatusbe constructed from a material such as stainless steel.

The improved service life resulting from the use of the improvedcleaning device and method of this invention is shown most clearly inTable I below wherein days of service of the improved cleaning deviceare shown for seven full size test electrolytic cells for themanufacture of sodium chloride by the electrolysis of a fused bathincluding sodium chloride and calcium chloride. The days of service aredays that the improved cleaning device of this invention, as describedin the drawings, remained in service on a 24-hour basis prior to removalfor the reasons shown under the column. For those cells having a listingof in service, it is meant that the improved cleaning device was stillin service and operating successfully at the time of the termination ofthe test to obtain the data for the table.

TABLE I Days Cleaning device Cell service Reason removed condition 61Diaphragm change No. 5 blade broken. 77 ...do OK. 70 Operator decisionOK. 17 Diaphragm change. N o. 5 blade broken. gig In service pipe havinga tickler assembly in combination therewith which includes a cleaningdevice extending into said riser pipe and driving means operablyconnected therewith for at least rotating said cleaning device, animproved cleaning device comprising, in combination,

(a) a rotatable elongated member extending centrally and substantiallyvertically from substantially the bottom through the top of said riserpipe for operable connection with said driving means,

(b) at least two arms mounted in vertical spaced relationshipsubstantially horizontally on and extending radially from said elongatedmember, and

(c) at least one vertical scraper bar movably mounted on the radialextension of a vertically adjacent pair of said at least two arms andextending therebetween, said at least one vertical scraper bar beingconstructed and arranged to have one: vertical side move toward saidriser pipe when said elongated member is rotated in one direction andsaid one vertical side move away from said riser pipe when saidelongated member is rotated in the opposite direction.

2. The apparatus of claim 1 further characterized by said one verticalside being provided with a substantially knife-like edge.

3. The apparatus of claim 1 further characterized by having a pluralityof vertical scraper bars attached to a plurality of arms and spacedalternately on opposite sides of said rotatable elongated member, eachof said plurality of vertical scraper bars being of suflicient length sothat the vertical distance encompassed by one vertical scraper baroverlaps the vertical distance encompassed by the next alternatevertical scraper bar.

4. The apparatus of claim 1 further characterized by said at least twoarms extending in the same radial direction from said rotatableelongated member.

5. The apparatus of claim 1 further characterized by said at least twoarms being slotted horizontally for mounting said at least one scraperbar.

6. The apparatus of claim 3 further characterized by the verticalscraper bar closest to the bottom of said riser pipe being rigidlyaflixed to said arms.

7. The apparatus of claim 5 further characterized by said at least twoarms having means for restricting the movement of said at least onevertical side away from said riser pipe.

References Cited UNITED STATES PATENTS 3,037,927 6/1962 Gallinger 204245JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner U.S.Cl. X.R. 204--68

